Search results for "absorption."
showing 10 items of 2682 documents
Ancient wood of the Acqualadrone rostrum: Materials history through gas chromatography/mass spectrometry and sulfur X-ray absorption spectroscopy
2012
In 2008 the rostrum from an ancient warship was recovered from the Mediterranean near Acqualadrone, Sicily. To establish its provenance and condition, samples of black and brown rostrum wood were examined using sulfur K-edge X-ray absorption spectroscopy (XAS) and gas chromatography/mass spectrometry (GC/MS). GC/MS of pyrolytic volatiles yielded only guaiacyl derivatives, indicating construction from pinewood. A derivatized extract of black wood yielded forms of abietic acid and sandaracopimaric acid consistent with pine pitch waterproofing. Numerical fits to the sulfur K-edge XAS spectra showed that about 65% of the endogenous sulfur consisted of thiols and disulfides. Elemental sulfur was…
Water Influences on the Copper Active Site in Hemocyanin
2010
Active metal sites play a key role in the biochemistry of oxygen transport by hemocyanins. Observing the changes in the local electronic structure of the copper sites upon oxygenation is thus essen...
X-ray Absorption under Operating Conditions for Solid-Oxide Fuel Cells Electrocatalysts: The Case of LSCF/YSZ
2019
We describe a novel electrochemical cell for X-ray absorption spectroscopy (XAS) experiments during electrical polarization suitable for high-temperature materials such as those used in solid oxide fuel cells. A half-cell LSCF/YSZ was then investigated under cathodic and anodic conditions (850 °
<title>Local structure of Ta-Re mixed oxide thin films studied by x-ray absorption spectroscopy</title>
2003
Mixed Ta-Re oxide thin films were synthesized for the first time by dc magnetron co-sputtering. Local environment around tantalum and rhenium atoms was studied by the Ta and Re L3-edges x-ray absorption spectroscopy in pure Ta2O5 and mixed Ta-Re oxide thin films (Ta:Re = 50:50, 38:62, 20:80 as determined from the ratio of the Ta-to-Re absorption edges). It was found that rhenium atoms are four-fold coordinated by oxygen atoms with R(Re-O) = 1.74 ± 0.01 Å and the mean square relative displacement (MSRD) σ2 = 0.0012 ± 0.0005 Å2. In pure Ta2O5 thin film, tantalum ions are coordinated by six oxygen atoms at R(Ta-O) = 2.02 ± 0.01 Å with the MSRD σ2 = 0.010 ± 0.001 Å2. The addition of rhenium ion…
Origin of Pressure-Induced Metallization in Cu 3 N: An X-ray Absorption Spectroscopy Study
2018
The authors are grateful to Professor Alain Polian for providing the NDAC cell.
Local Structure of Supported Keggin and Wells-Dawson Heteropolyacids and Its Influence on the Catalytic Activity
2019
[EN] Keggin [PW12O40]3– and Wells–Dawson [P2W18O62]6– heteropolyanions are nanosized transition-metal-oxygen clusters belonging to the heteropolyacids (HPAs) family. They are widely used as catalysts due to their high Brønsted acidity, and their dispersion on solid supports favors the accessibility to their acid sites generally increasing the catalytic activity. A series of binary materials composed of Keggin or Wells–Dawson HPAs and SiO2, TiO2, and ZrO2 have been prepared by impregnation or solvothermal methods. Remarkable differences have been found in the catalytic activities among the unsupported and supported HPAs. These differences have been correlated in the past to the structural ch…
Local structure studies of SrTi16O3and SrTi18O3
2014
In this work we report on the local structure of Ti in SrTi 16 O3 (STO16) and SrTi 18 O3 (STO18) investigated in the low temperature range (6‐300K) by extended x-ray absorption fine structure and x-ray absorption near edge structure (XANES) spectroscopy at Ti K-edge and by optical second harmonic generation (SHG). By comparing XANES of STO16 and STO18 we have identified the isotopic effect which produces at T < 100K a noticeable difference in the measured mean square relative displacements (MSRD) of Ti‐O1 bonds: while STO16 follow the expected Einstein-like behavior, for STO18 we have measured an increase of MSRD values with decreasing temperature. This is an indication of an increasing off…
X-ray Spectroscopy of (Ba,Sr,La)(Fe,Zn,Y)O3-δIdentifies Structural and Electronic Features Favoring Proton Uptake
2020
Mixed protonic–electronic conducting oxides are key functional materials for protonic ceramic fuel cells. Here, (Ba,Sr,La)(Fe,Zn,Y)O3−δ perovskites are comprehensively investigated by X-ray spectroscopy (in oxidized and reduced states). Extended X-ray absorption fine structure shows that Zn,Y doping strongly increases the tendency for Fe–O–Fe buckling. X-ray absorption near-edge spectroscopy at the Fe K-edge and X-ray Raman scattering at the O K edge demonstrate that both iron and oxygen states are involved when the samples are oxidized, and for the Zn,Y doped materials, the hole transfer from iron to oxygen is less pronounced. This can be correlated with the observation that these material…
Using photoelectron emission microscopy with hard-X-rays
2001
We present several successful test cases of using photoelectron emission microscopy (PEEM) for photon energy up to 25 keV. First, the full extended X-ray absorption fine structure analysis was implemented in areas as small as 100 mum(2) for transition-metal K edge absorption spectra and, therefore, demonstrated the feasibility of combining structural and chemical analysis with hard-X-ray absorption spectroscopy with high lateral resolution. We also show that PEEM can be used in a transmission (radiography) mode as an imaging detector for hard-X-ray, This approach again leads to the unprecedented 0.3 mum lateral resolution, particularly critical for the use of coherence-based phase contrast …
Jahn-Teller distortion aroundFe4+inSr(FexTi1−x)O3−δfrom x-ray absorption spectroscopy, x-ray diffraction, and vibrational spectroscopy
2007
$\mathrm{Sr}({\mathrm{Fe}}_{x}{\mathrm{Ti}}_{1\ensuremath{-}x}){\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}$ perovskites (strontium titanate ferrite solid solution) with well-defined oxygen stoichiometry have been studied as a function of iron concentration by x-ray diffraction, Fe and Ti $K$-edge x-ray absorption spectroscopy (XAS), and vibrational (Raman and infrared) spectroscopy. In reduced $\mathrm{Sr}({\mathrm{Fe}}_{x}{\mathrm{Ti}}_{1\ensuremath{-}x}){\mathrm{O}}_{3\ensuremath{-}x∕2}$ samples, the analysis of the Fe $K$-edge extended x-ray absorption fine structure indicates the expected presence of oxygen vacancies ${\mathrm{V}}_{\mathrm{O}}^{∙∙}$ in the first coordination shell…